08 - Conditional Statements in JavaScript.md

Conditional Statements in JavaScript

Introduction

Conditional Statements are used to make decisions in JavaScript.

They allow a program to execute different blocks of code depending on whether a condition is true or false.

JavaScript provides the following conditional statements:

1. if Statement
2. if...else Statement
3. if...else if...else Statement
4. switch Statement

---

1. if Statement

The if statement executes a block of code only when the specified condition is true.

Syntax

if(condition){
    // code to execute
}

Example

var age = 18;

if(age >= 18){
    console.log("You are eligible to vote.");
}

Output

You are eligible to vote.

Explanation

• The condition is:

age >= 18

• If the condition is true, the code inside the if block is executed.
• Since age is 18, the message is displayed.

---

2. if...else Statement

The else statement executes when the if condition is false.

Syntax

if(condition){

    // Executes if condition is true

}
else{

    // Executes if condition is false

}

---

Example

var age = 15;

if(age >= 18){

    console.log("Eligible to Vote");

}
else{

    console.log("Not Eligible to Vote");

}

Output

Not Eligible to Vote

---

Explanation

Since:

15 >= 18

is false,

the else block is executed.

---

3. if...else if...else Statement

This statement is used when there are multiple conditions.

Syntax

if(condition1){

    // code

}
else if(condition2){

    // code

}
else{

    // code

}

---

Example

var age = 16;

if(age >= 18){

    console.log("You are eligible to vote.");

}
else if(age >= 16){

    console.log("You are eligible for a learner's permit.");

}
else{

    console.log("You are not eligible.");

}

Output

You are eligible for a learner's permit.

---

Explanation

First Condition:

age >= 18

Result:

false

Second Condition:

age >= 16

Result:

true

Hence the second block executes.

---

Another Example

var marks = 82;

if(marks >= 90){

    console.log("Grade A");

}
else if(marks >= 75){

    console.log("Grade B");

}
else if(marks >= 50){

    console.log("Grade C");

}
else{

    console.log("Fail");

}

Output

Grade B

---

4. switch Statement

The switch statement is used as an alternative to multiple if-else statements.

It checks the value of an expression and executes the matching case.

---

Syntax

switch(expression){

    case value1:

        // code

        break;

    case value2:

        // code

        break;

    default:

        // code

}

---

Example

var day = "Monday";

switch(day){

    case "Monday":

        console.log("Today is Monday.");

        break;

    case "Tuesday":

        console.log("Today is Tuesday.");

        break;

    case "Wednesday":

        console.log("Today is Wednesday.");

        break;

    default:

        console.log("It's not Monday, Tuesday, or Wednesday.");

}

---

Output

Today is Monday.

---

Explanation

The switch statement compares:

day

with:

"Monday"

Since both are equal,

this block executes:

console.log("Today is Monday.");

The break statement stops further execution.

---

Importance of break Statement

Consider:

var day = "Monday";

switch(day){

    case "Monday":

        console.log("Monday");

    case "Tuesday":

        console.log("Tuesday");

    case "Wednesday":

        console.log("Wednesday");

}

Output

Monday

Tuesday

Wednesday

Because there is no break statement, all remaining cases execute.

---

With break

var day = "Monday";

switch(day){

    case "Monday":

        console.log("Monday");

        break;

    case "Tuesday":

        console.log("Tuesday");

        break;

}

Output

Monday

---

Nested if Statement

An if statement inside another if statement is called Nested if.

Example

var age = 20;

var citizen = true;

if(age >= 18){

    if(citizen == true){

        console.log("Eligible to Vote");

    }

}

Output

Eligible to Vote

---

Comparison Between if-else and switch

if-else	switch
Used for conditions	Used for fixed values
Supports relational operators	Uses exact matching
Suitable for ranges	Suitable for menu options
Slower for many conditions	Faster and cleaner

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Important Points

1. Conditional statements control the flow of execution.
2. if executes only when the condition is true.
3. else executes when the condition is false.
4. else if is used for multiple conditions.
5. switch is an alternative to multiple if-else statements.
6. break stops further execution in switch.
7. default executes when no case matches.

---

Summary

Conditional Statements are one of the most important concepts in JavaScript. They help programmers make decisions, validate conditions, execute different code blocks, and control program flow. The if, else, else if, and switch statements are widely used in web development for form validation, authentication systems, menu-driven programs, and business logic implementations.